I. Field of the Invention
This invention relates generally to a cardiac pacing lead designed for placement in a coronary vein, and more particularly to such a lead employing as an anchoring device a radially expandable polymer matrix member for holding the distal end portion of the pacing lead carrying the stimulating electrode in place.
II. Discussion of the Prior Art
Cardiac pacemakers for treating bradycardia commonly employ pacing leads for connecting an electrical pulse generator to excitable cardiac tissue, usually within the heart's right ventricle. Such leads have one or more electrodes proximate the distal end thereof and also commonly employ tines located just distal of the tip electrode for holding that electrode in contact with endocardial tissue in the right ventricle. The tines engage the trabeculae, resisting movement of the lead tip due to body movement and/or contractions of the heart muscle itself.
More recently, researchers have found that cardiac stimulation can have a beneficial effect in treating patients suffering from congestive heart failure (CHF). By properly controlling the AV interval of the pacemaker, a sick heart may be made to pump more efficiently. Pacing therapy for the treatment of CHF, however, often requires the ability to stimulate the left ventricle, either alone or in conjunction with right ventricular stimulation. Current methods for achieving left ventricular pacing require placement of an epicardial lead, via thoracotomy or a thoracoscopic approach. Because of the usual poor condition of CHF patients, both of these procedures are "high risk" due to the trauma of the surgery itself and the need for general anesthesia. To obviate the need for a thoracotomy, left ventricular access (LVA) leads have been developed that may be introduced through the coronary sinus and then advanced through the coronary veins so that the lead's stimulating electrode can be positioned on the surface of the left ventricle near the apex of the heart.
Those skilled in the art knowing the anatomical configuration and dimensions of the coronary veins on the heart can appreciate that a lead to be routed therethrough must be of a relatively small diameter as compared to a conventional pacing lead adapted for placement in the right ventricle. Heart motion and respiratory motion as well as blood blow or other body movement are typical mechanisms for lead dislodgment. As such, a means must be provided for at least temporarily anchoring the electrode at a desired selected location until tissue ingrowth and resulting lead stabilization occurs. Additionally, a means must be provided to decouple the relative motion of the heart from the distal tip of the lead thereby reducing trauma to the coronary vein and neighboring myocardium. These problems are deemed to be more acute in CHF patients due to the dilated condition of CHF hearts and general diseased state of the tissue.
It can be seen, then, that a need exists for a pacing lead that can readily be advanced through the coronary sinus and thence through a coronary vein on the heart and having an anchoring and stress-relieving structure for safely maintaining the electrode at a desired site notwithstanding heart motion, respiratory motion blood flow and other body movement.